Electro-oxidation of methanol and ethanol on carbon-supported Pt catalyst at intermediate temperature

Operation of a direct alcohol fuel cell (DAFC) at relatively high temperature is a key issue in this study from the standpoint of achieving high performance. To evaluate the temperature effect on the electro-oxidation of alcohols in an intermediate temperature region around 250 degrees C, a comparative kinetic study on the electro-oxidation of methanol and ethanol on carbon supported Pt was conducted using a single cell fabricated with CsH2PO4 proton conducting solid electrolyte. Current density of ethanol oxidation at 250 degrees C is comparable to that of methanol oxidation at low potentials (< 400 mV vs. reversible hydrogen electrode (RHE)). The apparent activation energy for methanol oxidation in the intermediate temperature region ranges from 80 to 60 kJ mol(-1) at examined potentials (200500 mV), while that for ethanol oxidation in the intermediate temperature region ranges from 60 to 35 U mol-1 at examined potentials (200-700 mV). The result suggests that the reaction mechanism of methanol oxidation changes with an increase in temperature from room temperature to around 250 degrees C. The possible mechanism of a rate-determining step at the intermediate temperature is discussed. In the case of ethanol, the electro-oxidation of intermediate species such as acetaldehyde is not accelerated even at intermediate temperatures. The oxidation of acetaldehyde will be a rate-determining step in the total electro-oxidation of ethanol on Pt/C at intermediate temperatures. (c) 2007 Elsevier B.V. All rights reserved.